1. Field of the Invention
The present invention relates generally to an optical disk device that records and reproduces information on an optical recording medium, such as a compact disk or a digital versatile disk, and a method of recording optical information.
2. Description of the Related Art
Recently, as the Internet becomes popularized by the development of information and communication technology, a lot of information has been interchanged through networks. Under such a circumstance, a read only optical device, such as a Compact Disk-Recordable (CD-R), and a recordable optical disk, such as a Compact Disk-Rewritable (CD-RW), attract attention as information recording media. Recently, as a semiconductor laser used as a laser source has a short wavelength, the diameter of a focus tends to be reduced due to a high Numerical Aperture (NA), objective lens having a high NA and a thin substrate is adopted, high capacity optical disks, such as a. Digital Versatile Disk-Recordable (DVD-R), a Digital Versatile Disk-Rewritable (DVD-RW) and a Digital Versatile Disk-Random Access Memory (DVD-RAM), are used as information recording media.
The recording of information on a CD-R is performed after record information obtained from a Personal Computer (PC) has been converted into Eight to Fourteen Modulation (EFM) signals. However, since a problem arises in that a mark is undesirably formed due to the heat accumulation and short cooling rate of an optical disk attributable to the difference in the composition of a dye recording layer constituting the optical disk, desired marks and spaces are not formed when the EFM signals are recorded.
Accordingly, a method of, with respect to a reference recording waveform, setting unique parameters for each of optical disks being used and maintaining a desired recording quality (hereinafter referred to as “write strategy”) is employed.
The write strategy is known to be related to a recording rate as well as the dye of an optical disk, a phase changing material, the film depth of, a dye, or the shape of a groove. Generally, for representative write strategies, there are a method of varying the ratio of a pit and a land, a method of adding an additional pulse to the front end of a recording pulse, a method of changing the rising or falling location of a pulse through the combination of a pit and a land, and a method of making the recording pulse a multi-pulse.
The method of varying the ratio of a pit to a land is implemented in such a way that the length of the pit is shortened at the time of low rate recording, and allows the shapes of the front and rear ends of a generated pit to be improved by irradiating a short pulse onto an optical disk using strong recording power.
The method of adding the additional pulse to the front end of the recording pulse is implemented in such a way that the irradiation of laser gives additional recording power to the front end of a pit difficult to be converted by heat, and allows the shape of the front end of the pit to be improved.
The method of changing the rising or falling location of a pulse using the combinations of pits and lands is to make the difference between the lengths of the pits and the lands uniforms for example, in such a way that the back end location of a land is changed according to the length of an antecedent land because the heat of the antecedent pit is transmitted to the land and influences a next pit, the front end location of the pit is changed according the length of a recording pit because the heat of the recording pit is transmitted to a position in front of the recording pit, the back end location of the pit is changed according to the length of the recording pit because the heat of the recording pit is transmitted to a location behind the recording pit, and the front end location of the land is changed according to the length of a posterior land because the heat of the posterior pit is transmitted to and influences a posterior land.
The method of making the recording pulse a multi-pulse is a method used in a phase change disk, such as a CD-RW, or a DVD. When information is recorded on the phase change disk using continuous pulses, the front end of a recorded pit is eliminated due to the action of heat, so-that the multi-pulse having cooling periods between the pits is used.
As described above, the write strategy is optimized and used for each of the optical disks because of a difference in the composition of a dye recording layer constituting the optical disk or a difference in a recording rate. Accordingly, a drive manufacturer requires various processes and a lot of time to optimize the write strategy.
Additionally, numerous kinds of optical disks that even the drive manufacturing companies are not aware of are sold commercially. Accordingly, it is impossible to prepare write strategies appropriate for all the optical disks currently distributed in the markets.
To solve the above problem, a method of recording a plurality of pieces of information, to which write strategies are converted, on a plurality of tracks, and selecting a write strategy, which allows a production jitter to be minimized, from the recorded write strategies (for example, refer to Japanese Unexamined Pat. Publication No. 2000-30254), or a method of recording information using a special recording pattern and obtaining the combination of a mark and a space having a minimum jitter value or deviation (for example, refer to Japanese Unexamined Pat. Publication No. 2000-30837).
The former method is problematic in that the write strategy finally selected is just the best write strategy in the set write strategies, so that the selected write strategy cannot always be an optimum write strategy. Furthermore, another problem arises in that only a recording region required for a test uses tracks.
Furthermore, the latter method is problematic in that in view of the use of a specific recording pattern, when a specific mark or space is changed, an influence on other marks and spaces are not taken into consideration, so that it is impossible to-set an optimum write strategy on, an optical disk being used through a single recording and reproducing test.